Honeycomb structural body

ABSTRACT

An object of the present invention is to provide a honeycomb structural body which is low in pressure loss and can prolong a period up to a regenerating process. The present invention is directed to a columnar honeycomb structural body comprising a large number of through holes placed in parallel with one another in a length direction with wall portion interposed therebetween, wherein: each of the through holes has one of ends sealed; one end face of the through hole differs in opening area from the other end face thereof; a ceramic material which constitutes the wall portion has an average pore diameter in a range from 5 to 30 μm; and the rate of capacity of micro pores each having a pore diameter two or more times larger than the average pore diameter is set to 30% or less of the capacity of the entire micro pores.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityto U.S. application Ser. No. 10/516,328, filed on Aug. 17, 2005, whichis a national stage of International Application No. PCT/JP04/08816filed on Jun. 23, 2004, which claims benefit of priority to JapanesePatent Application No. 2003-178713, filed on Jun. 23, 2003. The contentsof those applications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a honeycomb structural body used forthe purpose of collecting particulates in exhaust gases discharged froman internal combustion engine such as a diesel engine or the like.

BACKGROUND ART

Recently, particulates contained in exhaust gases discharged frominternal combustion engines of vehicles, such as buses, trucks and thelike, and construction machines and the like have raised seriousproblems as those particulates are harmful to the environment and thehuman body.

Conventionally, there have been proposed various ceramic filters whichallow exhaust gases to pass through porous ceramics to collectparticulates in the exhaust gases, thereby purifying the exhaust gases.

As such a ceramic filter, as shown in FIG. 7, there has been known ahoneycomb filter 120, which is prepared as a honeycomb structural bodymade of silicon carbide and the like, and has a structure in which aplurality of square-pillar shaped porous ceramic members 130 arecombined with one another through a sealing material layer 124 thatserves as an adhesive to form a ceramic block 125, and a sealingmaterial layer 123 is also formed on the circumference of this ceramicblock 125 so as to prevent leakage of exhaust gases.

The honeycomb filter 120 uses the porous ceramic members 130 having astructure as shown in FIG. 8 as constituent components, and a partitionwall 133, which are formed therein to separate through holes 131 a largenumber of which are placed in parallel with one another in the lengthdirection, functions as filters.

In other words, as shown in FIG. 8( b), each of the through holes 131,formed in the porous ceramic member 130, is sealed with a sealing member132 at one of ends of its exhaust gas inlet side or outlet side, so thatexhaust gases that have entered one through hole 131 are discharged fromanother through hole 131 after having always passed through a partitionwall 133 that separates the through holes 131.

Here, as described above, the sealing material layer 123, formed on theperiphery, is provided for the purpose of preventing exhaust gases fromleaking from the peripheral portion of the ceramic block 125, when thehoneycomb filter 120 is installed in an exhaust passage of an internalcombustion engine.

Since the honeycomb filter 120 of such a structure has superior heatresistance and provides easy regenerating processes and the like, it hasbeen applied to various large-size vehicles and vehicles with dieselengines. In other words, when the honeycomb filter 120 having such astructure is installed in the exhaust passage of an internal combustionengine, particulates in exhaust gases discharged from the internalcombustion engine are captured by the partition wall 133 upon passingthrough the honeycomb filter 120, so that the exhaust gases arepurified.

Moreover, with respect to such a type of honeycomb filter, disclosed isa structure in which the opening area on the exhaust gas inlet side ismade larger than the opening area on the exhaust gas outlet side, sothat the area of the wall portion through which exhaust gases pass perunit volume is made larger so as to improve the effective volume servingas the filter (for example, see Patent Literatures 1 to 12).

FIG. 9 schematically shows a cross-section perpendicular to the lengthdirection of an exhaust gas filter disclosed in Patent Literature 1 (seeFIG. 3 of Patent Literature 1).

In this exhaust gas filter 310, the respective through holes have thesame size, and the number of through holes 312, which are sealed at theexhaust gas inlet side, is made smaller than the number of through holes311, which are sealed at the exhaust gas outlet side. With thisarrangement, the opening area on the exhaust gas inlet side is madelarger than the opening area on the exhaust gas outlet side, so that theeffective volume serving as the filter is improved.

FIG. 10 schematically shows a cross-section perpendicular to the lengthdirection of an exhaust gas filter disclosed in Patent Literature 2 (seePatent Literature 2).

In this exhaust gas filter 320, the opening area and the number ofthrough holes 322, which are sealed at the exhaust gas inlet side, aremade different from the opening area and the number of through holes321, which are sealed at the exhaust gas outlet side. Thus, the openingarea on the exhaust gas inlet side is made larger than the opening areaon the exhaust gas outlet side, so that the effective volume serving asthe filter is improved.

FIG. 11 schematically shows a cross-section perpendicular to the lengthdirection of an exhaust gas filter disclosed in Patent Literature 1 (seeFIG. 17 of Patent Literature 1).

In this exhaust gas filter 330, the opening area of through holes 332,which are sealed at the exhaust gas inlet side, is made different fromthe opening area of through holes 331, which are sealed at the exhaustgas outlet side.

Moreover, in this filter, the number of the through holes 332 and thenumber of the through holes 331 are the same, and the through holes 331,which are sealed at the exhaust gas outlet side, are mutually made inface-contact with each other through a partition wall. Also in the caseof the exhaust gas filter having this structure, the opening area on theexhaust gas inlet side is made larger than the opening area on theexhaust gas outlet side, so that the effective volume serving as thefilter is improved.

FIG. 12 schematically shows a cross-section perpendicular to the lengthdirection of an exhaust gas filter disclosed in Patent Literature 3 (seeFIG. 5p of Patent Literature 3).

In this exhaust gas filter 340, the opening area of through holes 342,which are sealed at the exhaust gas inlet side, is made different fromthe opening area of through holes 341, which are sealed at the exhaustgas outlet side.

Moreover, in this filter, the number of the through holes 342 and thenumber of the through holes 341 are the same, and the through holes 341,which are sealed at the exhaust gas outlet side, are constituted not tohave face-contact with each other through a partition wall. Also in thecase of the exhaust gas filter having this structure, the opening areaon the exhaust gas inlet side is made larger than the opening area onthe exhaust gas outlet side, so that the effective volume serving as thefilter is improved.

In these conventional filters, the opening area on the gas inlet side ismade larger than the opening area on the gas outlet side, so that theeffective filtering area of the partition wall is made greater; thus, itbecomes possible to collect a large amount of particulates. Moreover, inthese filters, an object thereof is to reduce a pressure loss uponcollecting the same amount of particulates in comparison with a filterin which, as shown in FIGS. 7 and 8, the cross-sectional shape of allthe through holes is a quadrangular shape and the opening area on thegas-inlet side and the opening area on the exhaust gas outlet side arethe same.

However, these conventional filters tend to fail to sufficiently achievethe latter object, that is, a reduction in a pressure loss uponcollecting the same amount of particulates.

In the above-mentioned filters, it is considered that the following fourfactors mainly give effects to the pressure loss.

More specifically, those factors are considered to include: (1) anaperture ratio on the exhaust gas inlet side (ΔPa), (2) friction uponpassage through through holes (gas inlet side through hole: ΔPb-1, gasoutlet side through hole: ΔPb-2), (3) resistance upon passage through apartition wall (ΔPC), and (4) resistance exerted upon passage throughcollected particulates (ΔPd). Here, among these, the effect exerted by(4) resistance exerted upon passage through collected particulates (ΔPd)is considered to be greatest.

Here, in the case of the filters having the structures shown in FIGS. 9to 12, the initial pressure loss (pressure loss in a state withoutparticulates collected) tends to become higher in comparison with thefilter in which, as shown in FIGS. 7 and 8, the cross-sectional shape ofall the through holes is a quadrangular shape and the opening area onthe exhaust gas inlet side and the opening area on the exhaust gasoutlet side are the same. The reason for this is because, although thepressure loss caused by ΔPa and ΔPb-1 is slightly reduced, the pressureloss caused by ΔPb-2 and ΔPc becomes higher.

Moreover, with respect to the pressure loss after collection ofparticulates in a filter having each of structures as shown in FIGS. 9to 12, the filters having the structures shown in FIGS. 9 to 11 have apartition wall commonly possessed by the gas flow-in through holes. Inthe filters having this structure, as shown in FIG. 13, exhaust gasesfirst flow from the gas flow-in through hole 1311 side to the gasflow-out through hole 1312 side through flow passages “a” via thepartition wall commonly possessed by the gas flow-in through hole 1311and the gas flow-out through hole 1312. At this time, particulates arecaptured by the partition wall commonly possessed by the gas flow-inthrough hole 1311 and the gas flow-out through hole 1312 (see FIG. 13(a)).

Thereafter, as the particulates 1313 are collected on the partition wallcommonly possessed by the gas flow-in through hole 1311 and the gasflow-out through hole 1312, so that the pressure loss in the partitionwall becomes higher due to ΔPd, and exhaust gases are allowed to flowfrom the gas flow-in through hole 1311 side to the gas flow-out throughhole 1312 side through flow passages “b” via a partition wall commonlypossessed by the gas flow-in through holes 1311 (see FIG. 13( b)).

In this case, of the partition wall commonly possessed by the gasflow-in through holes 1311, it is considered that: the exhaust gasesstart to flow at the portion closest to the partition wall commonlypossessed by the gas flow-in through hole 1311 and the gas flow-outthrough hole 1312; and the gas flow-in portion gradually expands tofinally allow the entire partition wall forming the gas flow-in throughhole 1311 to serve as an effective filtering region.

FIGS. 13( a) and 13(b) are schematic diagrams for describing flowpassages of exhaust gases in the conventional filters.

In a honeycomb structural body of this type, when the amount ofparticulates accumulated on the partition wall commonly possessed by thegas flow-in through hole 1311 and the gas f low-out through hole 1312 islarge, it has been difficult to reduce the pressure loss upon collectionof particulates.

Moreover, Patent Literatures 3 and 4 disclose a filter in which anaverage porosity is more than 10% or less and pores have an average porediameter of 2 to 15 μm, with individual pore diameters distributed inthe almost entire range from 0.5 to 70 μm.

The present inventors have also studied methods for increasing the porediameter in order to reduce the pressure loss. However, as a result ofthe studies, it has been found that unexpectedly, even when the porediameter is made larger, the pressure loss is not lowered.

-   Patent Literature 1: JP-B 03-49608 (1991) (FIGS. 3, 17 and the    like), U.S. Pat. No. 4,417,908, JP-A 58-196820 (1983)-   Patent Literature 2: JP-U 58-92409 (1983)-   Patent Literature 3: U.S. Pat. No. 4,364,761 (FIG. 5p and the like),    JP-A 56-124417 (1981), JP-A 62-96717 (1987)-   Patent Literature 4: U.S. Pat. No. 4,276,071-   Patent Literature 5: U.S. Pat. No. 4,420,316-   Patent Literature 6: U.S. Pat. No. 4,420,316-   Patent Literature 7: JP-A 58-150015 (1983)-   Patent Literature 8: JP-A05-68828 (1993), Japanese Patent No.    3130587-   Patent Literature 9: FR2789327-   Patent Literature 10: WO02/100514-   Patent Literature 11: WO02/10562, DE10037403-   Patent Literature 12: WO03/20407, US Patent 2003-41730, U.S. Pat.    No. 6,696,132

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present inventors have examined a structure which can not be seen inthe conventional technique, in which the rate of micro pores havingrelatively larger pore diameters in comparison with an average porediameter is reduced with respect to the pore distribution as a whole.Thus, they have found that: by adopting the above-mentioned structure ina honeycomb structural body in which the sealing is made so as to makedifference in the aperture ratio, it becomes possible to allow exhaustgases to flow inmost efficiently, to reduce the pressure loss, and alsoto prolong the period up to a regenerating process. Thus, the presentinvention has been achieved.

Means for Solving the Problems

The present invention is directed to a columnar honeycomb structuralbody comprising a large number of through holes placed in parallel withone another in a length direction with a wall portion interposedtherebetween, wherein:

each of the through holes has one of ends sealed;

one end face of the through hole differs in opening area from the otherend face thereof;

a ceramic material which constitutes the wall portion has an averagepore diameter in a range from 5 to 30 μm; and

the rate of capacity of micro pores each having a pore diameter two ormore times larger than the average pore diameter is set to 30% or lessof the capacity of the entire micro pores.

Hereinafter, description will be given of the honeycomb structural bodyof the present invention.

In the honeycomb structural body of the present invention, the ceramicmaterial which constitutes the wall portion has an average pore diameterin a range from 5 to 30 μm, and the rate of capacity of micro pores,each having a pore diameter two or more times larger than the averagepore diameter, is set to 30% or less of the capacity of the entire micropores; therefore, as shown in FIG. 14, particulates are prevented frompenetrating into deep portions in the wall portion 82, so that theapparent thickness “d” (thickness 81 of a particulate layer determinedby taking into consideration the particulates deposited inside thepartition wall as well) of the particulates becomes thinner.

Moreover, since particulates are prevented from penetrating into deepportions in the wall portion, the particulates are accumulated on onlythe surface layer portion of a portion that easily transmits gasesbecause of its structure (for example, a portion of a partition wallthat separates a through hole having an opening on its gas inlet sideand a through hole having an opening on its gas outlet side and thelike) in a short period of time. With this arrangement, therefore, froman early stage with little amount of collection of particulates, notonly the portion that easily transmits gases because of its structure,but also a portion that hardly transmits gases because of its structure(for example, a portion of a partition wall that separates through holeshaving openings on the gas inlet sides and the like), is allowed totransmit gases, thereby making it possible to increase the effectivefiltering area.

Moreover, since the particulates are hardly allowed to penetrate intothe inner portions of the wall portion, the resistance exerted uponpassing through the wall portion hardly increases. As a result, thedegree of an increase in the pressure loss after collection ofparticulates is made smaller, making it possible to prolong a period upto the regenerating process.

In the honeycomb structural body of the present invention, when theopening area on the gas inlet side is made larger than the opening areaon the gas outlet side, the filtering area serving as the filter becomeslarger, making it possible to improve the collecting performance forparticulates.

Effects of the Invention

The honeycomb structural body of the present invention makes it possibleto prevent particulates from penetrating into deeper portions in thewall portion and, consequently, to make the apparent thickness of theparticulates thinner as well as allowing particulates to accumulate onlyon the surface portion of a portion that easily transmits gases becauseof its structure; thus, with this arrangement, even from an early stagewith little amount of collection of particulates, not only the portionthat easily transmits gases because of its structure, but also a portionthat hardly transmits gases because of its structure, is allowed totransmit gases, thereby making it possible to increase the effectivefiltering area.

Moreover, since the particulates are hardly allowed to penetrate intothe inner portions of the wall portion, the resistance exerted uponpassing through the wall portion hardly increases. As a result, thedegree of an increase in the pressure loss after collection ofparticulates is made smaller, making it possible to prolong a period upto the regenerating process.

In the honeycomb structural body of the present invention, when theopening area on the gas inlet side is made larger than the opening areaon the gas outlet side, the filtering area serving as the filter becomeslarger, making it possible to improve the collecting performance forparticulates.

EMBODIMENTS OF THE INVENTION

The present invention is related to a columnar honeycomb structural bodycomprising a large number of through holes placed in parallel with oneanother in a length direction with a wall portion interposedtherebetween, wherein:

each of the through holes has one of ends sealed;

one end face of the through hole differs in opening area from the otherend face thereof;

a ceramic material which constitutes the wall portion has an averagepore diameter in a range from 5 to 30 μm; and

the rate of capacity of micro pores each having a pore diameter two ormore times larger than the average pore diameter is set to 30% or lessof the capacity of the entire micro pores.

The honeycomb structural body of the present invention has a columnarstructure in which a large number of through holes are placed inparallel with one another in the length direction with a wall portioninterposed therebetween. The honeycomb structural body may be formed bycombining a plurality of columnar porous ceramic members, each having aplurality of through holes that are placed in parallel with one anotherin the length direction with a partition wall interposed therebetween,with one another through sealing material layers (hereinafter, alsoreferred to as an aggregated honeycomb structural body), or may beformed by ceramic members that are integrally sintered as one unit as awhole (hereinafter, also referred to as an integrated honeycombstructural body). Here, the honeycomb structural body may have a coatlayer formed on the circumference thereon.

In the case of the aggregated honeycomb structural body, the wallportion is constituted by a partition wall that separates through holesof porous ceramic members from each other and a sealing material layerthat serves as an adhesive layer between the porous ceramic members. Inthe case of the integrated honeycomb structural body, the wall portionis formed by a partition wall of one kind. In the following description,both of the partition wall and the sealing material layer are referredto as a wall portion without discrimination, unless the discriminationis required.

FIG. 1 is a perspective view that schematically shows a specific exampleof an aggregated honeycomb structural body as one example of thehoneycomb structural body of the present invention, FIG. 2( a) is aperspective view that schematically shows one example of a porousceramic member that forms the honeycomb structural body shown in FIG. 1,and FIG. 2( b) is a cross-sectional view taken along line A-A of theporous ceramic member shown in FIG. 2( a).

As shown in FIG. 1, the honeycomb structural body 10 of the presentinvention has a structure in which a plurality of porous ceramic members20 are combined with one another through a sealing material layer 14 toform a ceramic block 15, with a sealing material layer 13 for preventingexhaust gas leak being formed on the periphery of this ceramic block 15.

Here, in the porous ceramic member 20, a large number of through holes21 are placed in parallel with one another in the length direction, andeach of the through holes 21 has its one of ends sealed with a plug 22.Here, a through hole 21 a with a relatively larger area in itscross-sectional area perpendicular to the length direction has its endon the exhaust gas outlet side sealed, and a through hole 21 b with arelatively smaller area in the cross-sectional area has its end on theexhaust gas inlet side sealed.

Therefore, the honeycomb structural body 10 has a structure in which theopening area on the exhaust gas inlet side is made larger than theopening area on the exhaust gas outlet side.

Here, in the ceramic member 20, a portion of the wall portion (partitionwall) 23 that separates the through hole 21 a having an opening on itsexhaust gas inlet side (hereinafter, also referred to as a gas flow-inthrough hole) and the through hole 21 b having an opening on its exhaustgas outlet side (hereinafter, also referred to as a gas flow-out throughhole) functions as a filter. In other words, exhaust gases that haveentered one of the gas flow-in through holes 21 a are allowed to flowout of other gas flow-out through holes 21 b after always passingthrough these portions of the wall portion (partition wall) 23 thatseparates the corresponding through holes from each other.

In the honeycomb structural body 10 shown in FIG. 1, the shape isprepared as a column shape; however, not particularly limited to thecolumn shape, the honeycomb structural body of the present invention mayhave any desired shape, such as an elliptical column shape and arectangular pillar shape, and any size.

In the honeycomb structural body of the present invention, the materialfor the porous ceramic material is not particularly limited, andexamples thereof include: nitride ceramics such as aluminum nitride,silicon nitride, boron nitride, titanium nitride and the like; carbideceramics such as silicon carbide, zirconium carbide, titanium carbide,tantalum carbide, tungsten carbide and the like; and oxide ceramics suchas alumina, zirconia, cordierite, mullite and the like. Moreover, thehoneycomb structural body of the present invention may be made of acomposite material of silicon and silicon carbide or the like, or may bemade of aluminum titanate. Among these, silicon carbide, which has highheat resistance, superior mechanical properties and high thermalconductivity, is desirably used.

Moreover, the porous ceramic member has an average pore diameter in arange from 5 to 30 μm, and the rate of capacity of micro pores eachhaving a pore diameter two or more times larger than the average porediameter is set to 30% or less of the capacity of the entire micropores.

Since the average pore diameter is set in a range from 5 to 30 μm,particulates are prevented from penetrating into deep portions in thewall portion, making the structural body less susceptible to cloggingdue to particulates.

The average pore diameter of less than 5 μm tends to cause clogging dueto particulates, resulting in an increase in the pressure loss. Incontrast, the average pore diameter exceeding 30 μm causes particulatesto penetrate into deep portions in the wall portion, failing to providethe effects of the present invention.

Moreover, since, in the porous ceramic member, the rate of capacity ofmicro pores each having a pore diameter two or more times larger thanthe average pore diameter is set to 30% or less of the capacity of theentire micro pores, it is possible to make the pore diametercomparatively uniform and, consequently, to maintain resistance causedupon passage of exhaust gases through the wall portion in a small level.

In other words, with respect to the pore distribution state of the wallmutually separating the through holes on the gas-inlet side and the gasoutlet side, by making micro pores having relatively larger porediameters smaller in the number so that the gases are intentionally madedifficult to flow, the gases are allowed to flow through the partitionwall separating the through holes on the gas inlet side from each otherin an early stage so that it becomes possible to reduce the pressureloss.

This mechanism that makes the pressure loss lower has not beensufficiently clarified; however, the mechanism is presumably describedas follows:

When the rate of capacity of micro pores each having a pore diameter twoor more times larger than the average pore diameter exceeds 30%, therate of pore diameters that are comparatively larger than the averagepore diameter becomes higher. Then, at the initial stage, that is, atthe stage immediately after collection of particulates, as shown in FIG.15, exhaust gases are allowed to enter the portions of the micro poreshaving greater pore diameters more easily. Consequently, particulatesare allowed to penetrate into deep portions in the partition wall 84(deep portions in micro pores).

Moreover, since the exhaust gases are allowed to flow easily, it ispossible to accumulate the particulates in deeper layer portions in highdensity. For this reason, although the apparent thickness “D” of theparticulate layer 83 (thickness of the particulate layer in a state withthe inside of the micro pore being filled with particulates) becomesthicker to make the initial pressure loss lower, the pressure losssometimes has an abrupt increase due to resistance (ΔPd) upon passage ofparticulates as the particulates accumulate.

As described above, when the rate of capacity of micro pores each havinga pore diameter two or more times larger than the average pore diameterexceeds 30%, with respect to the capacity of the entire micro pores, thepressure loss of the filter increases consequently. Here, arrowsindicate flows of exhaust gases.

Moreover, as described above, after particulates have been sufficientlyaccumulated in the partition wall separating the gas inlet side throughhole and the gas outlet side through hole, particulates are also allowedto flow through the partition wall separating the gas flow-in throughholes from each other.

In contrast, in the honeycomb structural body of the present invention,with respect to the pore distribution state of the wall portionseparating the through holes on the gas inlet side and the gas outletside, by making micro pores having relatively larger pore diameterssmaller in the number so that the gases are intentionally made difficultto flow in comparison with the case in which micro pores having a largepore diameter are formed. As a result, exhaust gases are allowed to flowthrough the partition wall separating the gas flow-in through holes fromeach other, in a relatively early stage; thus, it becomes possible toavoid an abrupt rise in the pressure loss due to the thickness ofparticulates, uneven collecting processes and the like.

Moreover, as described with reference to FIG. 14, in the filter of thistype, since the thickness of particulates to be accumulated on thepartition wall is made thinner, it becomes possible to prevent aninsufficient regenerating process due to difficulty in burningparticulates and damages in a filter due to thermal impact caused by anabrupt burning process.

Here, the pore diameter can be measured through known methods, such as amercury injection method, and a measuring method using a scanningelectronic microscope (SEM).

When it is taken into consideration that the present invention needs tomeasure the entire pore diameter distribution, the pore diameter isdesirably measured through the mercury injection method.

In the same manner as the honeycomb structural body 10 shown in FIG. 1,the opening area on the exhaust gas inlet side is desirably made largerthan the opening area on the exhaust gas outlet side. This structuremakes it possible to expand the filtering area as the filter, andconsequently to improve the particulate collecting performance.

Further, in the above-mentioned honeycomb structural body, it ispreferable to provide the partition wall that separates through holes onthe gas inlet side from each other.

This structure makes it possible to ensure a wider effective filteringarea while maintaining a low pressure loss.

In the honeycomb structural body of the present invention, the porosityof the porous ceramic member is desirably set in a range from 30 to 70%.

This structure makes it possible to maintain sufficient strength in theporous ceramic member, to make particulates difficult to enter thepartition wall and, consequently, to maintain resistance caused uponpassage of exhaust gases through the partition wall in a low level.

The porosity of less than 30% tends to cause clogging in the partitionwall in an early stage, while the porosity exceeding 70% tends to causedegradation in the porous ceramic member; thus, it might be easilybroken.

Here, the above-mentioned porosity can be measured through known methodssuch as a mercury injection method, Archimedes method and a measuringmethod using a scanning electronic microscope (SEM).

In the honeycomb structural body of the present invention, the thicknessof the wall portion is desirably set in a range from 0.1 to 0.5 mm. Thisstructure makes it possible to maintain sufficient strength in theporous ceramic member and, consequently, to maintain resistance causedupon passage of exhaust gases through the partition wall in a low level.

The thickness of less than 0.1 mm tends to cause insufficient strengthin the honeycomb structural body, while the thickness exceeding 0.5 mmtends to cause a great increase in the pressure loss.

Moreover, in the honeycomb structural body of the present invention, theopening (through holes) on a cross-section perpendicular to the lengthdirection desirably has a density in a range from 15.5 to 62.0 pcs/cm².

In the case where the density is less than 15.5 pcs/cm², since the totalarea of the wall portion becomes smaller to cause a reduction in thefiltering efficiency as well as a reduction in the strength of thehoneycomb structural body depending on the thickness of the wallportion. In the case where the density exceeds 62.0 pcs/cm², therespective opening areas (through holes) on the gas inlet side and thegas outlet side become small, causing a reduction in the filterefficiency; in particular, when the opening (through hole) area on thegas-inlet side is smaller, the pressure loss tends to become greater.

With respect to the particle size of ceramic particles to be used uponmanufacturing the porous ceramic members, although not particularlylimited, those which are less susceptible to shrinkage in the succeedingfiring process are desirably used, and for example, those particles,prepared by combining 100 parts by weight of particles having an averageparticle size from 0.3 to 50 μm with 5 to 65 parts by weight ofparticles having an average particle size from 0.1 to 1.0 μm, aredesirably used. By mixing ceramic powders having the above-mentionedrespective particle sizes at the above-mentioned blending ratio, it ispossible to provide a porous ceramic member.

Moreover, by adjusting the particle sizes of the above-mentioned twokinds of powders, in particular, the particle size of the powder havingthe greater particle size, the pore diameter of the porous ceramicmember can be adjusted in the above-mentioned range. In the case wherean integrated honeycomb structural body is manufactured, the same methodcan be used.

Furthermore, a pore forming material having a uniform particle size maybe mixed in the material, and the resulting mixture is fired, so that aporous ceramic member having an adjusted pore diameter may bemanufactured. Here, the pore-forming material refers to a material usedfor forming pores in a processed ceramic material and, for example,those materials which are eliminated through a firing process may belisted.

The above-mentioned plug is desirably made of porous ceramics.

In the honeycomb structural body of the present invention, since theporous ceramic member with one end sealed with the plug is made ofporous ceramics, by making the plug using the same porous ceramics asthe porous ceramic member, it becomes possible to increase the bondingstrength between the two materials, and by adjusting the porosity of theplug similarly to that of the above-mentioned porous ceramic member, itis possible to take the matching of the coefficient of thermal expansionof the porous ceramic member and the coefficient of thermal expansion ofthe plug; thus, it becomes possible to prevent the occurrence of a gapbetween the plug and the partition wall due to a thermal stress that isexerted upon production as well as upon use and the occurrence of acrack in the plug or the portion of the partition wall with which theplug comes in contact.

In the case where the plug is made of porous ceramics, with respect tothe material thereof, not particularly limited, the same material as theceramic material which constitutes the porous ceramic member may beused.

In the honeycomb structural body of the present invention, the sealingmaterial layers (a wall portion) 13, 14 are formed between the porousceramic members 20 as well as on the periphery of the ceramic block 15.Further, the sealing material layer (a wall portion) 14, formed betweenthe porous ceramic members 20, also serves as an adhesive that bonds aplurality of porous ceramic members 20 to one another, and the sealingmaterial layer (a wall portion) 13, formed on the periphery of theceramic block 15, serves as a sealing material used for preventing leakof exhaust gases from the peripheral portion of the ceramic block 15,when the honeycomb structural body 10 of the present invention isinstalled in an exhaust passage of an internal combustion engine.

With respect to the material which constitutes the sealing materiallayer, not particularly limited, for example, a material composed of aninorganic binder, an organic binder and inorganic fibers and/orinorganic particles, or the like, may be used.

Here, as described above, in the honeycomb structural body of thepresent invention, the sealing material layer is formed between theporous ceramic members as well as on the periphery of the ceramic block;and these sealing material layers may be made of the same material ormaterials different from each other. Moreover, in the case where thesealing material layers are made of the same material, the blendingratios of the materials may be the same or different from each other.

With respect to the inorganic binder, for example, silica sol, aluminasol and the like may be used. Each of these may be used alone or two ormore kinds of these may be used in combination. Among the inorganicbinders, silica sol is more desirably used.

With respect to the organic binder, examples thereof include polyvinylalcohol, methyl cellulose, ethyl cellulose, carboxymethyl cellulose andthe like. Each of these may be used alone or two or more kinds of thesemay be used in combination. Among the organic binders, carboxymethylcellulose is more desirably used.

With respect to the inorganic fibers, examples thereof include ceramicfibers such as silica-alumina, mullite, alumina, silica and the like.Each of these may be used alone or two or more kinds of these may beused in combination. Among the inorganic fibers, silica-alumina fibersare more desirably used.

With respect to the inorganic particles, examples thereof includecarbides, nitrides and the like, and specific examples include inorganicpowder or whiskers made of silicon carbide, silicon nitride, boronnitride and the like. Each of these may be used alone, or two or morekinds of these may be used in combination. Among the inorganic fineparticles, silicon carbide having superior thermal conductivity isdesirably used.

The sealing material layer may be made of a dense material or may bemade of a porous material.

FIG. 3( a) is a perspective view that schematically shows a specificexample of an integrated honeycomb structural body as one example of thehoneycomb structural body of the present invention, and FIG. 3( b) is across-sectional view taken along line B-B of FIG. 3( a).

As shown in FIG. 3( a), the honeycomb structural body 30 is made of acolumnar porous ceramic block 35 in which a large number of throughholes 31 are placed in parallel with one another in the length directionwith a partition wall 33 interposed therebetween. Each of the throughholes 31 has its one of the ends sealed with a plug 32. Here, thethrough hole 31 a, which has a relatively larger cross-sectional areaperpendicular to the length direction, has its end on the exhaust gasoutlet side sealed so as to serve as the gas flow-in through hole, andthe through hole 31 b, which has a relatively smaller cross-sectionalarea, has its end on the exhaust gas inlet side sealed so as to serve asthe gas flow-out through hole.

Although not shown in FIG. 3, a sealing material layer may be formed onthe circumference of the porous ceramic block 35 in the same manner asthe honeycomb structural body 10 shown in FIG. 1.

Except that the porous ceramic block 35 has an integrated structureformed through a sintering process, the honeycomb structural body 30 hasthe same structure as the aggregated honeycomb structural body 10.Therefore, also in the honeycomb structural body 30, the partition wall33 that separates the gas flow-in through hole 31 a and the gas flow-outthrough hole 31 b is allowed to function as a filter, so that exhaustgases that have entered the gas flow-in through holes 31 a are allowedto flow out of the gas flow-in through holes 31 b after always passingthrough the partition wall 33.

Therefore, the integrated honeycomb structural body 30 also has the sameeffects as those of the aggregated honeycomb structural body.

In the same manner as the aggregated honeycomb structural body 10, inthe integrated honeycomb structural body 30, the porous ceramic block 35has an average pore diameter in a range from 5 to 30 μm and the rate ofcapacity of micro pores each having a pore diameter two or more timeslarger than the average pore diameter is set to 30% or less of thecapacity of the entire micro pores. Further, the shape and size of theintegrated honeycomb structural body 30 may also be determineddesirably, and the porosity thereof is desirably set in a range from 30to 70% in the same manner as the aggregated honeycomb structural body.

Moreover, the density of openings (through holes) on the cross-sectionperpendicular to the length direction and the thickness of the wallportion are desirably set in the same manner as the aggregated honeycombstructural body.

With respect to the porous ceramics which constitute the porous ceramicblock 35, not particularly limited, the same nitride, carbide and oxideceramics used in the aggregated honeycomb structural body may beproposed, and in general, oxide ceramics such as cordierite and the likeare desirably used.

The plug 32 to be used in the integrated honeycomb structural body 30 isalso desirably made of porous ceramics, and with respect to the materialthereof, although not particularly limited, for example, the samematerials as the ceramic materials used for forming the above-mentionedporous ceramic block 35 may be used.

In the above-mentioned honeycomb structural body having the structure asshown in FIGS. 1 and 3, although not particularly limited, the shape ofa cross-section perpendicular to the length direction of each of thosethrough holes is desirably formed into a polygonal shape.

This polygonal shape eliminates portions of the through hole that causegreater friction when exhaust gases are allowed to pass through thethrough hole due to the shape of the through hole and, consequently,reduces a pressure loss caused by the friction of exhaust gases uponpassing through the through hole, and also eliminates portions of apartition wall with irregular thicknesses, that is, portions thatlocally make it difficult for exhaust gases to pass through, so as toreduce a pressure loss caused by resistance of a partition wall exertedwhen exhaust gases pass through the partition wall; thus, the polygonalshape is allowed to exert either of the above-mentioned effects.

Moreover, among polygonal shapes, a polygonal shape of a quadrangle ormore is desirably used, and at least one of the corners is desirablyformed as an obtuse angle. With this arrangement, it becomes possible toreduce a pressure loss caused by friction of exhaust gases upon flowingthrough the through hole inlet side and friction of exhaust gases uponflowing through the through hole outlet side.

The vicinity of each of corners on the cross-section of the through holeis desirably formed by a curved line. By forming the corner into acurved line, it becomes possible to prevent occurrence of cracks causedby a stress concentration at the corner.

Here, the opening area on the exhaust gas inlet side is desirably madelarger than the opening area on the exhaust gas outlet side; and in thiscase, the ratio of the opening area on the exhaust gas inlet side andthe opening area on the exhaust gas outlet side (the opening area on theexhaust gas inlet side/the opening area on the exhaust gas outlet side,hereinafter, also referred to simply as opening area ratio) is desirablyset in a range from 1.01 to 6.

When the ratio of areas exceeds 6, the capacity of the through holes onthe exhaust gas outlet side becomes too small; thus, the pressure loss,caused by friction upon passing through the through holes and resistanceupon passing through the partition wall, increases to cause an increasein the initial pressure loss, resulting in an increase in the initialpressure loss. The ratio of the areas is desirably set in a range from1.2 to 5. More desirably, the ratio of the areas is set in a range from1.2 to 3.0.

FIGS. 4( a) to 4(d) as well as FIGS. 5( a) to 5(f) are cross-sectionalviews each of which schematically shows one portion of the cross-sectionof a porous ceramic member constituting the aggregated honeycombstructural body in accordance with the present invention. Here,regardless of the integrated type and the aggregated type, the shapes ofthe cross-sections of the respective through holes are the same;therefore, referring to these Figures, the cross-sectional shapes in thehoneycomb structural body of the present invention are described.

In FIG. 4( a), the ratio of opening areas is almost 1.55, in FIG. 4( b),it is almost 2.54, in FIG. 4( c), it is almost 4.45 and in FIG. 4( d),it is almost 6.00. Moreover, in FIGS. 5( a), 5(c) and 5(e), all theratios of opening areas are almost 4.45, and in FIGS. 5( b), 5(d) and5(f), all the ratios of opening areas are almost 6.00.

In FIGS. 4( a) to 4(d), each of the cross-sectional shapes of the gasflow-in through holes is an octagon, and each of the cross-sectionalshapes of the gas flow-out through holes is a quadrangle (square), andthese are alternately arranged; thus, by changing the cross-sectionalarea of each of the gas flow-out through holes, with the cross-sectionalshape of each of the gas flow-in through holes being slightly changed,it is possible to desirably change the ratio of opening areas easily. Inthe same manner, with respect to the honeycomb filter shown in FIG. 5,the ratio of opening areas can be desirably changed.

Here, in honeycomb structural bodies 160 and 260 shown in FIGS. 5( a)and 5(b), each of the cross-sectional shapes of the gas flow-in throughholes 161 a and 261 a is a pentagon with three corners thereof being setto almost right angles, and each of the cross-sectional shapes of thegas flow-in through holes 161 b and 261 b is a quadrangle, and therespective quadrangles are placed at portions of a greater quadrangle,which diagonally face each other. Honeycomb structural bodies 170 and270, shown in FIGS. 5( c) and 5(d), have modified shapes of thecross-sections shown in FIGS. 4( a) to 4(d) so that a portion of thepartition wall commonly possessed by each of the gas flow-in throughholes 171 a, 271 a and each of the gas flow-in through holes 171 b, 271b is expanded toward the gas flow-in through hole side with a certaincurvature. This curvature may be desirably set.

In this case, the curved line, which forms a portion of the partitionwall commonly possessed by each of the gas flow-in through holes 171 a,271 a and each of the gas flow-in through holes 171 b, 271 b,corresponds to ¼ of a circle.

In honeycomb structural bodies 180 and 280 shown in FIGS. 5( e) to 5(f),the gas flow-in through holes 181 a, 281 a and the gas flow-in throughholes 281 b, 281 b are formed into quadrangles (rectangular shapes), andas shown in Figures, these through holes are arranged so that, when thetwo gas flow-in through holes and the two gas flow-in through holes arecombined with one another, an almost square shape is formed.

Moreover, the cross-sectional shapes of the through holes forming thehoneycomb structural body of the present invention may have the shapesthat have already shown in FIGS. 9 to 12.

Therefore, in the honeycomb structural body of the present invention,the opening area of the gas flow-in through holes may be made greaterthan the opening area of the gas flow-out through holes, and the numbersof the gas flow-in through holes and the gas flow-out through holes maybe different.

In the present invention, the distance between centers of gravity ofcross-sections perpendicular to the length direction of adjacentlylocated gas flow-in through holes is desirably designed to be equal tothe distance between centers of gravity of cross-sections perpendicularto the length direction of adjacently located gas flow-out throughholes.

The term “the distance between centers of gravity of the cross-sectionsof adjacent gas flow-in through holes” represents the smallest distancebetween the center of gravity on a cross-section perpendicular to thelength direction of one gas flow-in through hole and the center ofgravity on a cross-section perpendicular to the length direction of anadjacent gas flow-in through hole; and the term “the distance betweencenters of gravity of the cross-sections of adjacent gas flow-outthrough holes” represents the smallest distance between the center ofgravity on a cross-section perpendicular to the length direction of onegas flow-out through hole and the center of gravity on a cross-sectionperpendicular to the length direction of an adjacent gas flow-outthrough hole.

In the case where the two distances between centers of gravity are equalto each other, since heat is uniformly dispersed upon regenerating, itis possible to prevent the temperature inside the honeycomb structuralbody from being locally distributed in a biased manner, and consequentlyto provide a filter having superior durability free from cracks causedby a thermal stress, even after long-term repetitive use.

When the honeycomb structural body of the present invention is used as afilter for collecting particulates in exhaust gases, collectedparticulates are gradually deposited on the inside of each of thethrough holes forming the honeycomb structural body.

Here, as the amount of deposited particulates becomes greater, thepressure loss increases gradually, and when it exceeds a predeterminedvalue, the load imposed on the engine becomes too high. Therefore, inthe present invention, the filter is regenerated by burning theparticulates, and in the case of the present invention, since the degreeof an increase in the pressure loss after collection of particulates ismade smaller in comparison with that of the conventional filter, itbecomes possible to prolong the period up to the regenerating process.

The following description will discuss one example of a manufacturingmethod for the honeycomb structural body of the present invention. Inthe case where the structure of the honeycomb structural body of thepresent invention is prepared as an integrated honeycomb structural bodyconstituted by one sintered body as a whole as shown in FIG. 3, first,an extrusion molding process is carried out by using the above-mentionedmaterial paste mainly composed of ceramics to manufacture a ceramicformed body having almost the same shape as the honeycomb structuralbody 30 shown in FIG. 3.

With respect to the material paste, not particularly limited, anymaterial paste may be used as long as the porous ceramic block that hasbeen manufactured is allowed to have an average pore diameter in a rangefrom 5 to 30 μm with the rate of capacity of micro pores each having apore diameter two or more times larger than the average pore diameterbeing set to 30% or less of the capacity of the entire micro pores, and,for example, a material, prepared by adding a binder and a dispersantsolution to powder with a predetermined particle size made of theaforementioned ceramics, may be used.

With respect to the above-mentioned binder, not particularly limited,examples thereof include:

methylcellulose, carboxy methylcellulose, hydroxy ethylcellulose,polyethylene glycol, phenolic resin and epoxy resin.

In general, the blended amount of the above-mentioned binder isdesirably set to 1 to 10 parts by weight with respect to 100 parts byweight of ceramic powder.

With respect to the dispersant solution, not particularly limited,examples thereof include: an organic solvent such as benzene; alcoholsuch as methanol; and water.

An appropriate amount of the above-mentioned dispersant solution ismixed therein so that the viscosity of the material paste is set withina fixed range.

These ceramic powder, binder and dispersant solution are mixed by anattritor or the like, and sufficiently kneaded by a kneader or the like,and then extrusion-molded so that the above-mentioned ceramic formedbody is manufactured.

Moreover, a molding auxiliary may be added to the material paste, ifnecessary.

With respect to the molding auxiliary, not particularly limited,examples thereof include: ethylene glycol, dextrin, fatty acid soap,polyalcohol and the like.

Furthermore, a pore-forming agent, such as balloons that are fine hollowspheres composed of oxide-based ceramics, spherical acrylic particlesand graphite, may be added to the above-mentioned material paste, ifnecessary.

With respect to the above-mentioned balloons, not particularly limited,for example, alumina balloons, glass micro-balloons, shirasu balloons,fly ash balloons (FA balloons) and mullite balloons may be used. Amongthese, fly ash balloons are more desirably used.

Next, after the above-mentioned ceramic formed body has been dried byusing a drier such as a microwave drier, a hot-air drier, a dielectricdrier, a reduced-pressure drier, a vacuum drier and a frozen drier,predetermined through holes are filled with plug paste to form plugs sothat a mouth sealing process for plugging the through holes is carriedout. Here, the sealing process is carried out so that the size of theopening area of the gas flow-in through holes is made larger than thesize of the opening area of the gas flow-out through holes.

With respect to the above-mentioned plug paste, not particularlylimited, for example, the same material paste as the above-mentionedmaterial paste may be used; however, those pastes, prepared by adding alubricant, a solvent, a dispersant and a binder to ceramic powder usedas the above-mentioned material paste, are desirably used. With thisarrangement, it becomes possible to prevent ceramics particles in theplug paste from settling in the middle of the sealing process.

Next, the ceramic dried body filled with the plug paste is subjected todegreasing and firing processes under predetermined conditions so that ahoneycomb structural body, made of porous ceramics and constituted by asingle sintered body as a whole, is manufactured.

Here, with respect to the degreasing and firing conditions and the likeof the ceramic dried body, it is possible to apply conditions that havebeen conventionally used for manufacturing a honeycomb structural bodymade of porous ceramics.

In the case where the structure of the honeycomb structural body of thepresent invention is prepared as an aggregated honeycomb structural bodyconstituted by a plurality of porous ceramic members combined with oneanother through sealing material layers as shown in FIG. 1, first, anextrusion molding process is carried out by using the above-mentionedmaterial paste mainly composed of ceramics to manufacture a raw ceramicformed body having a shape like a porous ceramic member 20 shown in FIG.2.

Here, with respect to the material paste, the same material paste asdescribed in the above-mentioned aggregated honeycomb structural bodymay be used.

After the above-mentioned raw molded body has been dried by using amicrowave drier or the like to form a dried body, plug paste, whichforms plugs, is injected into predetermined through holes of the driedbody so that sealing processes for sealing the through holes are carriedout.

Here, with respect to the plug paste, the same plug paste as thatdescribed in the above-mentioned integrated honeycomb structural bodymay be used, and with respect to the sealing process, the same method asthe method for the above-mentioned integrated honeycomb structural bodymay be used except that the subject to be filled with the plug paste isdifferent.

In this case also, the sealing processes are desirably carried out sothat the size of opening areas of the gas flow-in through holes is madelarger than the size of opening areas of the gas flow-out through holes.

Next, the dried body that has been subjected to the sealing process issubjected to degreasing and firing processes under predeterminedconditions so that a porous ceramic member in which a plurality ofthrough holes are placed in parallel with one another in the lengthdirection with a partition wall interposed therebetween is manufactured.

Here, with respect to the conditions and the like of degreasing andfiring processes for the raw molded body, those conditionsconventionally used for manufacturing a honeycomb structural bodyconstituted by a plurality of porous ceramic members that are combinedwith one another through sealing material layers may be used.

Next, sealing material paste to be used for forming a sealing materiallayer 14 is applied with an even thickness to form a sealing materialpaste layer, and on this sealing material paste layer, a process forlaminating another porous ceramic member 20 is successively repeated sothat a laminated body of porous ceramic members 20 having a rectangularpillar shape with a predetermined size is manufactured.

With respect to the material for forming the sealing material paste,since the same material as that described in the honeycomb structuralbody of the present invention can be used, the description thereof willnot be given herein.

Next, the laminated body of the porous ceramic members 20 is heated sothat the sealing material paste layer is dried and solidified to formthe sealing material layer 14; thereafter, by cutting the peripheralportion into, for example, a shape as shown in FIG. 1, by using adiamond cutter or the like so that a ceramic block 15 is manufactured.

A sealing material layer 13 is formed on the circumference of theceramic block 15 by using the sealing material paste so that a honeycombstructural body in which a plurality of porous ceramic members arecombined with one another through sealing material layers ismanufactured.

Any of the honeycomb structural bodies thus manufactured have a pillarshape, and the structures thereof are shown in FIG. 1 and FIG. 2.

With respect to the application of the honeycomb structural body of thepresent invention, although not particularly limited, it is desirablyused for exhaust gas purifying devices for use in vehicles.

FIG. 6 is a cross-sectional view that schematically shows one example ofan exhaust gas purifying device for use in vehicles, which is providedwith the honeycomb structural body of the present invention.

As shown in FIG. 6, an exhaust gas purifying device 800 is mainlyconstituted by a honeycomb structural body 80 of the present invention,a casing 830 that covers the external portion of the honeycombstructural body 80, a holding sealing material 820 that is placedbetween the honeycomb structural body 80 and the casing 830 and heatingmeans 810 placed on the exhaust gas inlet side of the honeycombstructural body 80, and an introducing pipe 840, which is connected toan internal combustion engine such as an engine, is connected to one endof the casing 830 on the exhaust gas inlet side, and an exhaust pipe 850externally coupled is connected to the other end of the casing 830. InFIG. 6, arrows show flows of exhaust gases.

Moreover, in FIG. 6, the honeycomb structural body 80 may be prepared asthe honeycomb structural body 10 shown in FIG. 1 or as the honeycombstructural body 30 shown in FIG. 3.

In the exhaust gas purifying device 800 having the above-mentionedarrangement, exhaust gases, discharged from the internal-combustionsystem such as an engine, are directed into the casing 830 through theintroducing pipe 840, and allowed to flow into the honeycomb structuralbody 80 through the through holes and to pass through the wall portion(a partition wall); thus, the exhaust gases are purified, withparticulates thereof being collected in the wall portion (a partitionwall), and are then discharged outside through the exhaust pipe 850.

After a large quantity of particulates have been accumulated on the wallportion (a partition wall) of the honeycomb structural body 80 to causean increase in pressure loss, the honeycomb structural body 80 issubjected to a regenerating process.

In the regenerating process, a gas, heated by using a heating means 810,is allowed to flow into the through holes of the honeycomb structuralbody 80 so that the honeycomb structural body 80 is heated to burn andeliminate the particulates deposited on the wall portion (a partitionwall).

Moreover, in the present invention, in addition to the above-mentionedmethod, the particulates may be burned and eliminated by using apost-injection system.

Moreover, the honeycomb structural body of the present invention mayhave a catalyst capable of purifying CO, HC, NOx and the like in theexhaust gases deposited in the pores.

When such a catalyst is supported thereon, the honeycomb structural bodyof the present invention is allowed to function as a honeycombstructural body capable of collecting particulates in exhaust gases, andalso to function as a catalyst converter for purifying CO, HC, NOx andthe like contained in exhaust gases. Moreover, depending on cases, thehoneycomb structural body makes it possible to lower the burningtemperature of the particulates.

With respect to the catalyst, examples thereof include noble metals suchas platinum, palladium and rhodium. The catalyst, made of a noble metalsuch as platinum, palladium or rhodium, is a so-called three-waycatalyst, and the honeycomb structural body of the present inventionwhich is provided with such a three-way catalyst is allowed to functionin the same manner as conventionally known catalyst converters.Therefore, with respect to the case in which the honeycomb structuralbody of the present invention also functions as a catalyst converter,detailed description thereof will not be given herein.

Here, with respect to the catalyst that is supported on the honeycombstructural body of the present invention, not particularly limited tothe above-mentioned noble metal, any catalyst may be supported thereon,as long as it can purify CO, HC, NOx and the like contained in exhaustgases.

EXAMPLES

The following description will discuss the present invention in detailby means of examples; however, the present invention is not intended tobe limited by these examples.

Example 1

(1) Powder of α-type silicon carbide having an average particle size of11 μm (±1 μm for the portion of 99.99% by weight thereof) (60% byweight), obtained by adjusting the grain size of a material using asieve, and powder of β-type silicon carbide having an average particlesize of 0.5 μm (40% by weight) were wet-mixed, and to 100 parts byweight of the resulting mixture were added and kneaded 5 parts by weightof an organic binder (methyl cellulose) and 10 parts by weight of waterto obtain a mixed composition. Next, after a slight amount of aplasticizer and a lubricant had been added and kneaded therein, theresulting mixture was extrusion-molded so that a raw formed product,which had almost the same cross-sectional shape as the cross-sectionalshape shown in FIG. 4( b) and a ratio of opening areas of 3.00, wasmanufactured.

(2) Next, the above-mentioned raw formed product was dried by using amicrowave drier or the like to form a ceramic dried body, and afterpredetermined through holes had been filled with a paste having the samecomposition as the raw formed product, the resulting product was againdried by using a drier, and then degreased at 400° C., and fired at2000° C. in a normal-pressure argon atmosphere for 3 hours tomanufacture a porous ceramic member, which was a silicon carbidesintered body, and had a porosity of 42%, an average pore diameter of 5μm, with a rate of capacity of micro pores (hereinafter, referred to aspore diameter distribution) each having a pore diameter two times largerthan the average pore diameter (10 μm in the present example) being setto 10%, a size of 34.3 mm×34.3 mm×150 mm, the number of through holes of31 pcs/cm² and a thickness of substantially all the wall portion (apartition wall) 23 of 0.4 mm.

Here, with respect to end faces of the porous ceramic member thusobtained, an end face on one side of each of through holes 41 a having arelatively large cross-sectional area was sealed with a plug, and an endface on the other side of each of through holes 41 b having a relativelysmaller cross-sectional area was sealed with a plug.

Here, the above-mentioned pore diameter was measured by using thefollowing method:

With respect to the porous ceramic member, the pore diameter (0.2 to 500μm) was measured by using a mercury injection method (in accordance withJIS R 1655:2003).

More specifically, a porous ceramic member having a honeycomb structurewas cut into cubes having a size of about 0.8 cm, and these were washedby using ultrasonic-wave with ion exchanged water, and sufficientlydried. Next, the pore diameter of these samples were measured by using aMicromeritics automatic porosimeter, AutoPore III9405, manufactured byShimadzu Corporation. In this case, the measuring range was set from 0.2to 500 μm, and in the range from 100 to 500 μm, the measurements werecarried out for every pressure unit of 0.1 psia, and in the range from0.2 to 100 μm, the measurements were carried out for every pressure unitof 0.25 psia. Thus, the pore diameter distribution and the total micropore capacity were calculated.

The average pore size (diameter) was calculated as, 4×S (integratedmicro pore area)/V(integrated micro pore capacity).

Moreover, the pore diameter of twice as large as the average porediameter was obtained, and the micro pore capacity of pores having thepore diameter exceeding the pore diameter of twice as large as theaverage was further calculated; moreover, based upon the measured dataof total micro pore range and the rate of the micro pore diametercalculated as described above, the rate of the capacity of micro poreshaving the pore diameter exceeding the pore diameter twice as large asthe average micro pore diameter, which relates to the present invention,was calculated.

Examples 2 to 12

Porous ceramic members were manufactured in the same manner as Example1, except that the average pore diameter and the pore diameterdistribution were changed to values as shown in Table 1. Here, theparticle size of the material powder, firing conditions and the like areshown in Table 1. Moreover, the particle size of the material powder(α-type silicon carbide powder) was set to ±1 μm for the portion of99.99% by weight thereof in the same manner as Example 1.

Comparative Examples 1 to 6

Porous ceramic members were manufactured in the same manner as Example1, except that the average pore diameter and the pore diameterdistribution were changed to values as shown in Table 1. Here, theparticle size of the material powder, firing conditions and the like areshown in Table 1.

With respect to each of the porous ceramic members according to Examples1 to 12 and Comparative Examples 1 to 6, respective ceramic blocks weremanufactured, and the following measurements were carried out. Here, themanufacturing method of the ceramic block is shown below:

First, by using a heat resistant sealing material paste containing 30%by weight of alumina fibers having a fiber length of 0.2 mm, 21% byweight of silicon carbide particles having an average particle size of0.6 μm, 15% by weight of silica sol, 5.6% by weight of carboxymethylcellulose and 28.4% by weight of water, a large number of the poroussilicon carbide members were combined with one another, and this wasthen cut by using a diamond cutter to form a cylindrical shaped ceramicblock.

In this case, the thickness of the sealing material layers used forcombining the porous ceramic members was adjusted to 1.0 mm.

Next, ceramic fibers made of alumina silicate (shot content: 3%, fiberlength: 0.1 to 100 mm) (23.3% by weight), which served as inorganicfibers, silicon carbide powder having an average particle size of 0.3 μm(30.2% by weight), which served as inorganic particles, silica sol (SiO₂content in the sol: 30% by weight) (7% by weight), which served as aninorganic binder, carboxymethyl cellulose (0.5% by weight), which servedas an organic binder, and water (39% by weight) were mixed and kneadedto prepare a sealing material paste.

Next, a sealing material paste layer having a thickness of 1.0 mm wasformed on the circumferential portion of the ceramic block by using theabove-mentioned sealing material paste. Further, this sealing materialpaste layer was dried at 120° C. so that a cylinder-shaped honeycombstructural body having a diameter of 144 mm and a length of 150 mm inthe length direction, to be used as a honeycomb filter for purifyingexhaust gases, was manufactured.

Further, the initial pressure loss and the pressure losses at theamounts of collected particulates of 0.5 g/l, 1 g/l, 2 g/l, 4 g/l, 6 g/land 8 g/l and the regenerating limit value of the above-mentionedcylinder-shaped honeycomb structural body were measured, and the resultsare shown in Table 1.

(Evaluation Method)

(1) Pressure Loss Measurement

As shown in FIG. 6, each of the honeycomb structural bodies of theexamples and comparative examples was placed in an exhaust passage of anengine to form an exhaust gas purifying device, and the engine wasdriven at the number of revolutions of 3000 min⁻¹ and a torque of 50 Nmso that the pressure losses in the initial state and upon collection ofa predetermined amount of particulates were measured.

(2) Measurement on Regenerating Limit Value

As shown in FIG. 6, each of the honeycomb structural bodies according tothe examples and comparative examples was placed in an exhaust passageof an engine to form an exhaust gas purifying device, and the engine wasdriven at the number of revolutions of 3000 min⁻¹ and a torque of 50 Nmfor a predetermined period of time so that samples that had collectedparticulates were obtained.

Next, the engine was driven at the number of revolutions of 4000 min⁻¹and a torque of 200 Nm, and when the filter temperature had becomeconstant in the vicinity of 700° C., the engine was maintained at thenumber of revolutions of 1050 min⁻¹ and a torque of 30 Nm so that theparticulates collected in the filter were forcefully burned. Thisexperiment was carried out in the same manner on several filters, andthe greatest amount of particulates that would cause no cracks wasmeasured, and the resulting value was determined as the regeneratinglimit value.

TABLE 1 Average Pore Regenerat- pore diameter Particle Firing Loss uponcollecting particulates ing limit diameter distribution Porositydiameter Mixing condition Initial 0.5 1 2 4 6 8 value (μm) (%) (%) (μm)ratio (° C.) loss g/l g/l g/l g/l g/l g/l g/l Example 1 5 10 42 11:0.560:40 2000 2.1 3.5 4.1 5.1 7 9.2 11.6 9.4 Example 2 5 20 40 13:0.5 60:402050 2.1 3.4 3.9 4.8 6.8 9 11.4 9.2 Example 3 5 30 40 15:0.5 60:40 20502 3.6 4.3 5.4 7.5 9.9 12.3 9 Example 4 10 10 42 10:0.5 60:40 2200 1.73.1 3.6 4.6 6.6 8.8 11.2 9.4 Example 5 10 20 40 20:0.5 60:40 2150 1.73.1 3.9 5 7 9.3 11.7 9.4 Example 6 10 30 38 30:0.5 60:40 2100 1.7 3.13.7 5.6 7.6 9.9 12.4 9.2 Example 7 20 10 42 25:0.5 60:40 2250 1.6 2.93.7 4.8 6.8 9.1 11.5 8.8 Example 8 20 20 40 30:0.5 60:40 2200 1.6 2.93.9 5.2 7.3 9.6 12 8.8 Example 9 20 30 38 40:0.5 60:40 2150 1.6 2.8 3.65.6 7.8 10.2 12.7 8.6 Example 10 30 10 42 40:0.5 60:40 2250 1.5 2.7 3.14.6 6.8 9.3 11.7 8.5 Example 11 30 20 40 50:0.5 60:40 2200 1.5 2.6 2.94.6 7.2 9.8 12.4 8.5 Example 12 30 30 38 60:0.5 60:40 2150 1.5 2.6 2.84.4 7.6 10.3 12.9 8.5 Comparative 0.5 10 42  3:0.5 60:40 1900 2.4 4.14.9 6.3 8.7 11.3 14.1 5.8 Example 1 Comparative 5 35 40 17:0.5 60:402050 2.1 3.7 4.6 6.1 8.4 11.1 13.9 8 Example 2 Comparative 10 35 3835:0.5 60:40 2100 1.8 3.2 3.7 5.9 8.3 10.8 13.6 8 Example 3 Comparative20 35 38 45:0.5 60:40 2100 1.6 2.7 3.5 6.2 8.5 11.2 14.1 7.9 Example 4Comparative 30 35 38 70:0.5 60:40 2130 1.5 2.5 3.1 4.7 8.5 11.3 14.4 7.8Example 5 Comparative 35 10 38 45:0.5 60:40 2250 1.5 2.4 3.1 4.6 8.210.8 13.9 7.8 Example 6 Note) Pore diameter distribution: the rate ofcapacity of micro pores having a pore diameter two or more times largerthan the average pore diameter.

As clearly indicated by Table 1, although there are some cases in whichthe initial pressure loss in the honeycomb structural bodies accordingto the comparative examples is lower than that of the honeycombstructural bodies according to the examples, the honeycomb structuralbodies according to the comparative examples generally have a higherpressure loss upon collection of 4 g/l of particulates in comparisonwith the honeycomb structural bodies of the examples, and the pressureloss upon collection of 8 g/l of particulates, is reduced to a low levelin the honeycomb structural bodies according to the examples.

This is presumably because particulates penetrate to reach deep layerportions in the wall portion in the honeycomb structural bodies of thecomparative examples, while particulates are collected by only surfacelayer portions of the wall portion in the honeycomb structural bodies ofthe examples.

Moreover, the honeycomb structural bodies according to the examples havea greater regenerating limit value in comparison with the filtersaccording to the comparative examples so that a larger amount ofparticulates can be collected up to the regenerating process; thus, itbecomes possible to prolong the period of time up to the regeneratingprocess.

Example 13

(1) The same processes as (1) of Example 1 were carried out to prepare amixed composition. Next, after a slight amount of a plasticizer and alubricant had been added to the mixed composition and further kneaded,the resulting mixed composition was subjected to an extrusion moldingprocess to manufacture a raw ceramic formed body having across-sectional shape as shown in FIG. 9 with a ratio of opening areasof 3.00. Here, the particle size of the material powder (α-type siliconcarbide powder) was set to ±1 μm for the portion of 99.99% by weightthereof in the same manner as Example 1.

(2) Next, the above-mentioned raw formed product was dried by using amicrowave drier or the like to form a ceramic dried body, and afterpredetermined through holes had been filled with a paste having the samecomposition as the raw formed product, the resulting product was againdried by using a drier, and then degreased at 400° C., and fired at2000° C. in a normal-pressure argon atmosphere for 3 hours tomanufacture a porous ceramic member, which was a silicon carbidesintered body, and had a porosity of 42%, an average pore diameter of 5μm, a pore diameter distribution of 10%, a size of 34.3 mm×34.3 mm×150mm, the number of through holes of 31 pcs/cm² and a thickness ofsubstantially all the wall portion (a partition wall) 23 of 0.4 mm.

Here, with respect to end faces of the porous ceramic member thusobtained, either one of end faces was sealed with a plug so as to adjustthe ratio of opening areas to the above-mentioned size.

Examples 14 to 17

The same processes as Example 13 were carried out except that theaverage pore diameter and the pore diameter distribution were set tovalues as shown in Table 2 to manufacture a porous ceramic member. Here,the particle size of the material powder (α-type silicon carbide powder)was set to ±1 μm for the portion of 99.99% by weight thereof in the samemanner as Example 1.

Comparative Examples 7 to 9

The same processes as Example 13 were carried out except that theaverage pore diameter and the pore diameter distribution were set tovalues as shown in Table 2 to manufacture a porous ceramic member. Here,the particle size of the material powder, the firing conditions and thelike are shown in Table 2.

The porous ceramic members according to Examples 14 to 17 andComparative Examples 7 to 9 were formed into cylinder-shaped honeycombstructural bodies having the same structure as that of Example 1, andthe initial pressure loss, the pressure loss upon collection of apredetermined amount of particulates and the regenerating limit valuewere respectively measured. The results are shown in Table 2.

Here, the measurements of the pore diameter and the like, themeasurements of the pressure loss and the measurements of theregenerating limit value were carried out by using the same methods asExample 1.

TABLE 2 Average Pore Regenerat- pore diameter Particle Firing Loss uponcollecting particulates ing limit diameter distribution Porositydiameter Mixing condition Initial 0.5 1 2 4 6 8 value (μm) (%) (%) (μm)ratio (° C.) loss g/l g/l g/l g/l g/l g/l g/l Example 13 5 10 42 11:0.560:40 2000 3.8 6.2 7.1 8.4 10.4 13.2 15.6 8.2 Example 14 10 10 42 10:0.560:40 2200 3.3 5.7 6.6 7.8 9.9 12.6 15.2 8 Example 15 10 20 40 20:0.560:40 2150 3.3 5.7 6.9 8.2 10.4 13.1 15.8 8 Example 16 10 30 38 30:0.560:40 2100 3.3 5.7 6.7 8.8 10.9 13.8 16.4 7.8 Example 17 30 10 42 40:0.560:40 2250 3 5.2 6.1 7.8 10.2 13.2 15.9 7.6 Comparative 0.5 10 42  3:0.560:40 1900 4.1 6.8 7.9 9.5 12.1 15.2 18.2 5.8 Example 7 Comparative 1035 38 35:0.5 60:40 2100 3.4 5.8 6.6 9.1 11.8 14.9 17.7 7.3 Example 8Comparative 35 10 38 45:0.5 60:40 2250 3 4.9 6.1 7.8 11.5 14.7 18.1 7.2Example 9 Note) Pore diameter distribution: the rate of capacity ofmicro pores having a pore diameter two or more times larger than theaverage pore diameter.

As clearly indicated by Table 2, although there are some cases in whichthe initial pressure loss in the honeycomb structural bodies accordingto the comparative examples is lower than that of the honeycombstructural bodies according to the examples, the honeycomb structuralbodies according to the comparative examples generally have a higherpressure loss upon collection of 4 g/l of particulates in comparisonwith the honeycomb structural bodies of the examples, and the pressureloss upon collection of 8 g/l of particulates is reduced to a low levelin the honeycomb structural bodies according to the examples.

This is presumably because particulates penetrate to reach deep layerportions in the wall portion in the honeycomb structural bodies of thecomparative examples, while particulates are collected by only surfacelayer portions of the wall portion in the honeycomb structural bodies ofthe examples.

Moreover, the honeycomb structural bodies according to the examples havea greater regenerating limit value in comparison with the filtersaccording to the comparative examples so that a larger amount ofparticulates can be collected up to the regenerating process; thus, itbecomes possible to prolong the period of time up to the regeneratingprocess.

Example 18

(1) The same processes as (1) of Example 1 were carried out to prepare amixed composition. Next, after a slight amount of a plasticizer and alubricant had been added to the mixed composition and further kneaded,the resulting mixed composition was subjected to an extrusion moldingprocess to manufacture a raw ceramic formed body having across-sectional shape as shown in FIG. 10 with a ratio of opening areasof 3.00. Here, the particle size of the material powder (α-type siliconcarbide powder) was set to ±1 μm for the portion of 99.99% by weightthereof in the same manner as Example 1.

(2) Next, the above-mentioned raw formed product was dried by using amicrowave drier or the like to form a ceramic dried body, and afterpredetermined through holes had been filled with a paste having the samecomposition as the raw formed product, the resulting product was againdried by using a drier, and then degreased at 400° C., and fired at2000° C. in a normal-pressure argon atmosphere for 3 hours tomanufacture a porous ceramic member, which was a silicon carbidesintered body, and had a porosity of 42%, an average pore diameter of 5μm, a pore diameter distribution of 10%, a size of 34.3 mm×34.3 mm×150mm, the number of through holes of 31 pcs/cm² and a thickness ofsubstantially all the wall portion (a partition wall) 23 of 0.4 mm.

Here, with respect to end faces of the porous ceramic member thusobtained, an end face on one side of each of through holes 321 having arelatively large cross-sectional area was sealed with a plug, and an endface on the other side of each of through holes 322 having a relativelysmaller cross-sectional area was sealed with a plug.

Examples 19 to 22

The same processes as Example 18 were carried out except that theaverage pore diameter and the pore diameter distribution were set tovalues as shown in Table 3 to manufacture a porous ceramic member. Here,the particle size of the material powder (α-type silicon carbide powder)was set to ±1 μm for the portion of 99.99% by weight thereof in the samemanner as Example 1.

Comparative Examples 10 to 12

The same processes as Example 18 were carried out except that theaverage pore diameter and the pore diameter distribution were set tovalues as shown in Table 3 to manufacture a porous ceramic member. Here,the particle size of the material powder, the firing conditions and thelike are shown in Table 3.

The porous ceramic members according to Examples 18 to 22 andComparative Examples 10 to 12 were formed into cylinder-shaped honeycombstructural bodies having the same structure as that of Example 1, andthe initial pressure loss, the pressure loss upon collection of apredetermined amount of particulates and the regenerating limit valuewere respectively measured. The results are shown in Table 3.

Here, the measurements of the pore diameter and the like, themeasurements of the pressure loss and the measurements of theregenerating limit value were carried out by using the same methods asExample 1.

TABLE 3 Average Pore Regenera- pore diameter Particle Firing Loss uponcollecting particulates ing limit diameter distribution Porositydiameter Mixing condition Initial 0.5 1 2 4 6 8 value (μm) (%) (%) (μm)ratio (° C.) loss g/l g/l g/l g/l g/l g/l g/l Example 18 5 10 42 11:0.560:40 2000 3.2 5.5 6.3 7.7 10.2 13.6 17.6 8.5 Example 19 10 10 42 10:0.560:40 2200 2.8 5.1 5.8 7.2 9.8 13.2 17.1 8.2 Example 20 10 20 40 20:0.560:40 2150 2.8 5.1 6 7.6 10.2 13.7 17.6 8.2 Example 21 10 30 38 30:0.560:40 2100 2.8 5.1 5.8 7.9 10.8 14.2 18.4 8 Example 22 30 10 42 40:0.560:40 2250 2.6 4.8 5.5 7.2 10 13.4 17.5 7.7 Comparative 0.5 10 42 3:0.560:40 1900 3.5 5.9 6.8 8.9 11.9 15.5 19.7 5.8 Example 10 Comparative 1035 38 35:0.5 60:40 2100 2.8 5.2 5.9 8.1 11.2 14.7 19 7.5 Example 11Comparative 35 10 38 45:0.5 60:40 2250 2.6 4.7 5.6 7.6 10.7 14.5 18.97.3 Example 12 Note) Pore diameter distribution: the rate of capacity ofmicro pores having a pore diameter two or more times larger than theaverage pore diameter.

As clearly indicated by Table 3, although there are some cases in whichthe initial pressure loss in the honeycomb structural bodies accordingto the comparative examples is lower than that of the honeycombstructural bodies according to the examples, the honeycomb structuralbodies according to the comparative examples generally have a higherpressure loss upon collection of 4 g/l of particulates in comparisonwith the honeycomb structural bodies of the examples, and the pressureloss upon collection of 8 g/l of particulates is reduced to a low levelin the honeycomb structural bodies according to the examples.

This is presumably because particulates penetrate to reach deep layerportions in the wall portion in the honeycomb structural bodies of thecomparative examples, while particulates are collected by only surfacelayer portions of the wall portion in the honeycomb structural bodies ofthe examples.

Moreover, the honeycomb structural bodies according to the examples havea greater regenerating limit value in comparison with the filtersaccording to the comparative examples so that a larger amount ofparticulates can be collected up to the regenerating process; thus, itbecomes possible to prolong the period of time up to the regeneratingprocess.

Example 23

(1) The same processes as (1) of Example 1 were carried out to prepare amixed composition. Next, after a slight amount of a plasticizer and alubricant had been added to the mixed composition and further kneaded,the resulting mixed composition was subjected to an extrusion moldingprocess to manufacture a raw ceramic formed body having across-sectional shape as shown in FIG. 12 with a ratio of opening areasof 3.00. Here, the particle size of the material powder (α-type siliconcarbide powder) was set to ±1 μm for the portion of 99.99% by weightthereof in the same manner as Example 1.

(2) Next, the above-mentioned raw formed product was dried by using amicrowave drier or the like to form a ceramic dried body, and afterpredetermined through holes had been filled with a plug paste having thesame composition as the raw formed product, the resulting product wasagain dried by using a drier, and then degreased at 400° C., and firedat 2000° C. in a normal-pressure argon atmosphere for 3 hours tomanufacture a porous ceramic member, which was a silicon carbidesintered body, and had a porosity of 42%, an average pore diameter of 5μm, a pore diameter distribution of 10%, a size of 34.3 mm×34.3 mm×150mm, the number of through holes of 31 pcs/cm² and a thickness ofsubstantially all the wall portion (the partition wall) 23 of 0.4 mm.

Here, with respect to end faces of the porous ceramic member thusobtained, an end face on one side of each of through holes 341 having arelatively large cross-sectional area was sealed with a plug, and an endface on the other side of each of through holes 342 having a relativelysmaller cross-sectional area was sealed with a plug.

Examples 24 to 27

The same processes as Example 23 were carried out except that theaverage pore diameter and the pore diameter distribution were set tovalues as shown in Table 4 to manufacture a porous ceramic member. Here,the particle size of the material powder (α-type silicon carbide powder)was set to ±1 μm for the portion of 99.99% by weight thereof in the samemanner as Example 1.

Comparative Examples 13 to 15

The same processes as Example 23 were carried out except that theaverage pore diameter and the pore diameter distribution were set tovalues as shown in Table 4 to manufacture a porous ceramic member. Here,the particle size of the material powder, the firing conditions and thelike are shown in Table 4.

The porous ceramic members according to Examples 23 to 27 andComparative Examples 13 to 15 were formed into cylinder-shaped honeycombstructural bodies having the same structure as that of Example 1, andthe initial pressure loss, the pressure loss upon collection of apredetermined amount of particulates and the regenerating limit valuewere respectively measured. The results are shown in Table 4.

Here, the measurements of the pore diameter and the like, themeasurements of the pressure loss and the measurements of theregenerating limit value were carried out by using the same methods asExample 1.

TABLE 4 Average Pore Regenerat- pore diameter Particle Firing Loss uponcollecting particulates ing limit diameter distribution Porositydiameter Mixing condition Initial 0.5 1 2 4 6 8 value (μm) (%) (%) (μm)ratio (° C.) loss g/l g/l g/l g/l g/l g/l g/l Example 23 5 10 42 11:0.560:40 2000 2.1 3.2 3.9 5.5 7.7 10.9 14.3 8 Example 24 10 10 42 10:0.560:40 2200 1.7 2.7 3.4 4.9 7.2 10.4 13.6 7.8 Example 25 10 20 40 20:0.560:40 2150 1.7 2.7 3.7 5.4 7.8 11 14.4 7.8 Example 26 10 30 38 30:0.560:40 2100 1.7 2.7 3.4 5.8 8.3 11.6 14.9 7.6 Example 27 30 10 42 40:0.560:40 2250 1.5 2.4 3 4.9 7.5 11.1 14.5 7.5 Comparative 0.5 10 42  3:0.560:40 1900 2.3 4.3 5.2 6.7 9.2 11.9 15.2 5.8 Example 13 Comparative 1035 38 35:0.5 60:40 2100 1.8 2.6 3.3 6.1 8.7 12.1 15.5 7.2 Example 14Comparative 35 10 38 45:0.5 60:40 2250 1.5 2.3 3.1 4.9 8.8 12.5 16.2 7Example 15 Note) Pore diameter distribution: the rate of capacity ofmicro pores having a pore diameter two or more times larger than theaverage pore diameter.

As clearly indicated by Table 4, although there are some cases in whichthe initial pressure loss in the honeycomb structural bodies accordingto the comparative examples is lower than that of the honeycombstructural bodies according to the examples, the honeycomb structuralbodies according to the comparative examples generally have a higherpressure loss upon collection of 4 g/l of particulates in comparisonwith the honeycomb structural bodies of the examples, and the pressureloss upon collection of 8 g/l of particulates, is reduced to a low levelin the honeycomb structural bodies according to the examples.

This is presumably because particulates penetrate to reach deep layerportions in the wall portion in the honeycomb structural bodies of thecomparative examples, while particulates are collected by only surfacelayer portions of the wall portion in the honeycomb structural bodies ofthe examples.

Moreover, the honeycomb structural bodies according to the examples havea greater regenerating limit value in comparison with the filtersaccording to the comparative examples so that a larger amount ofparticulates can be collected up to the regenerating process; thus, itbecomes possible to prolong the period of time up to the regeneratingprocess.

Moreover, in all the examples and comparative examples, with respect: tohoneycomb structural bodies according to Example 3 and ComparativeExample 2; to Example 6 and Comparative Example 3; to Example 9 andComparative Example 4; to Example 16 and Comparative Example 8; toExample 21 and Comparative Example 11; as well as to Example 26 andComparative Example 14, the pressure losses upon collection of 8 g/l ofparticulates are compared with each other, and in the case of thehoneycomb structural bodies having a partition wall that separate gasflow-in through holes as shown in FIGS. 4 and 9, by reducing the porediameter distribution to 30% or less, the pressure loss is reduced to92% or less in comparison with the case in which the pore diameterdistribution exceeds 30% (in the case of 35%); in contrast, in the caseof the honeycomb structural bodies having no partition wall thatseparate gas flow-in through holes as shown in FIGS. 10 and 12, when thepore diameter distribution is reduced to 30% or less, the pressure lossreduction remains at about 95% in comparison with the case in which thepore diameter distribution exceeds 30% (in the case of 35%). Moreover,in the case where the pressure losses upon collection of 4 g/l and 6 g/lof particulates were compared with each other, the same results wereobtained.

This shows that the effects of the present invention are remarkablyexerted in the honeycomb structural body having a partition wall thatseparate gas flow-in through holes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing a specific example ofan aggregated honeycomb structural body as one example of a honeycombstructural body of the present invention.

FIG. 2( a) is a perspective view schematically showing one example of aporous ceramic member which constitutes the honeycomb structural bodyshown in FIG. 1; and FIG. 2( b) is a cross-sectional view taken alongline A-A of the porous ceramic member shown in FIG. 2( a).

FIG. 3( a) is a perspective view schematically showing a specificexample of an integrated honeycomb structural body as another example ofthe honeycomb structural body of the present invention; and FIG. 3( b)is a cross-sectional view taken along line B-B thereof.

FIGS. 4( a) to 4(d) are cross-sectional views each schematically showinga part of a cross-section of the porous ceramic member which constitutesthe aggregated honeycomb structural body of the present invention.

FIGS. 5( a) to 5(f) are cross-sectional views each schematically showinga part of a cross-section of the porous ceramic member which constitutesthe aggregated honeycomb structural body of the present invention.

FIG. 6 is a cross-sectional view schematically showing one example of anexhaust gas purifying device for a vehicle in which the honeycombstructural body of the present invention is installed.

FIG. 7 is a perspective view schematically showing a conventionalhoneycomb structural body.

FIG. 8( a) is a perspective view schematically showing a ceramic membercontained in the conventional honeycomb structural body; and FIG. 8( b)is a cross-sectional view taken along line B-B of FIG. 8( a).

FIG. 9 schematically shows a cross-section perpendicular to a lengthdirection of an exhaust gas filter.

FIG. 10 schematically shows a cross-section perpendicular to the lengthdirection of the exhaust gas filter.

FIG. 11 schematically shows a cross-section perpendicular to the lengthdirection of the exhaust gas filter.

FIG. 12 schematically shows a cross-section perpendicular to the lengthdirection of the exhaust gas filter.

FIGS. 13( a) and 13(b) are schematic diagrams for describing exhaust gasflow paths in a conventional filter.

FIG. 14 is a conceptual diagram schematically showing the thickness ofparticulates when the particulates have been deposited on a wall portionin the honeycomb structural body of the present invention.

FIG. 15 is a conceptual diagram schematically showing the thickness ofparticulates when the particulates have been deposited on a wall portionin a conventional filter.

EXPLANATION OF SYMBOLS

-   10, 30 honeycomb structural body-   13, 14 sealing material layer-   15, 35 ceramic block-   20, 40, 50, 70 porous ceramic member-   21 a, 31 a, 41 a, 51 a, 71 a gas flow-in through hole-   21 b, 31 b, 41 b, 51 b, 71 b gas flow-out through hole-   22, 32 plug-   23, 43, 53, 73 wall portion (partition wall)-   33 wall portion-   160, 170, 180, 260, 270, 280 honeycomb structural body-   161 a, 171 a, 181 a, 261 a, 271 a, 281 a gas flow-in through hole-   161 b, 171 b, 181 b, 261 b, 271 b, 281 b gas flow-out through hole-   163, 173, 183, 263, 273, 283 wall portion

1. A columnar honeycomb structural body, comprising: a porous ceramicblock having a plurality of through holes and a wall portion interposedbetween the through holes, the through holes extending in parallel withone another in a length direction of the porous ceramic block, whereinthe through holes have one of ends sealed such that an opening area ofone end face of the through holes is larger than an opening area of theother end face of the through holes, the plurality of through holesincludes a plurality of large through holes sealed on the one end faceand a plurality of small through holes sealed on the other end face, thelarge through holes have cross-section areas which are larger thancross-section areas of the small through holes, the large through holesand the small through holes are positioned such that the wall portionincludes a plurality of partition wall portions each of which isinterposed between two adjacent large through holes of the large throughholes and a plurality of partition wall portions each of which isinterposed between adjacent large through hole and small through hole ofthe large and small through holes, that each of the partition wallportions between the two adjacent large through holes is defined by twoadjacent sides of the two adjacent large through holes, that each of thepartition wall portions between the adjacent large and small throughholes is defined by two adjacent sides of the adjacent large and smallthrough holes, and that a distance between centers of gravity of thecross-section areas of adjacent ones of the large through holes is setto be equal to a distance between centers of gravity of thecross-section areas of adjacent ones of the small through holes, each ofthe partition wall portions between the adjacent large and small throughholes has a length which is greater than a length of each of thepartition wall portions between the two adjacent large through holes,the opening area of the one end face of the through holes and theopening area of the other end face of the through holes have a ratio ina range between 1.01 to 6, the wall portion has a plurality of micropores having an average pore diameter in a range from 5 to 30 μm, themicro pores include large micro pores having a pore diameter two or moretimes larger than the average pore diameter, and the large micro poreshave a capacity of which a rate is set to 30% or less of a capacity ofthe micro pores in entirety.
 2. The honeycomb structural body accordingto claim 1, wherein the opening area on a gas inlet side is made largerthan the opening area on a gas outlet side.
 3. The honeycomb structuralbody according to claim 1, wherein each of the large through holes hasan octagonal cross-section shape and each of the small through holes hasa quadrangle cross-section shape.
 4. The honeycomb structural bodyaccording to claim 1, wherein the wall portion has a porosity in a rangefrom 30 to 70%.
 5. The honeycomb structural body according to claim 1,wherein the plurality of through holes on a cross-section perpendicularto the length direction has a density in a range from 15.5 to 62.0pcs/cm².
 6. The honeycomb structural body according to claim 1, whereinthe porous ceramic block comprises silicon carbide.
 7. The honeycombstructural body according to claim 1, wherein the wall portion has athickness in a range from 0.1 to 0.5 mm.
 8. An exhaust gas purifyingdevice for a vehicle, comprising the honeycomb structural body accordingto claim
 1. 9. The honeycomb structural body according to claim 2,wherein the wall portion has a porosity in a range from 30 to 70%. 10.The honeycomb structural body according to claim 2, wherein theplurality of through holes on a cross-section perpendicular to thelength direction has a density in a range from 15.5 to 62.0 pcs/cm². 11.The honeycomb structural body according to claim 2, wherein the porousceramic block comprises silicon carbide.
 12. The honeycomb structuralbody according to claim 2, wherein the wall portion has a thickness in arange from 0.1 to 0.5 mm.
 13. An exhaust gas purifying device for avehicle, comprising the honeycomb structural body according to claim 2.14. The honeycomb structural body according to claim 4, wherein theplurality of through holes on a cross-section perpendicular to thelength direction has a density in a range from 15.5 to 62.0 pcs/cm². 15.The honeycomb structural body according to claim 4, wherein the porousceramic block comprises silicon carbide.
 16. The honeycomb structuralbody according to claim 4, wherein the wall portion has a thickness in arange from 0.1 to 0.5 mm.
 17. An exhaust gas purifying device for avehicle, comprising the honeycomb structural body according to claim 4.18. The honeycomb structural body according to claim 5, wherein theporous ceramic block comprises silicon carbide.
 19. The honeycombstructural body according to claim 5, wherein the wall portion has athickness in a range from 0.1 to 0.5 mm.
 20. An exhaust gas purifyingdevice for a vehicle, comprising the honeycomb structural body accordingto claim 5.